Power source device

The present invention relates to a power source device used in a printer and the like.

Conventionally, a power source device of this kind is disclosed in Japanese Patent Application Unexamined Publication No. H10-295086. FIG. 9 is a circuit diagram illustrating a configuration of a conventional power source device. As shown in FIG. 9, transistors 3 and 4 are connected to DC power source 2 via input terminal 1, and output terminal 7 and load 8 such as a roller of a printer are connected to a connecting node between transistors 3 and 4 via transformer 5 and low-pass filter 6.

Next, an operation of a conventional power source device configured as mentioned above is described. FIG. 10 shows ideal voltage waveforms to illustrate an operation of a conventional power source device. Voltage waveform G of output terminal 7 as shown in FIG. 10 is detected by voltage detecting circuit 9 and input into a negative input end of comparator 10, and an ideal alternating output voltage signal from alternating signal generator 11 is input into a positive input end of comparator 1, thereby carrying out comparison. Then, comparator 10 can obtain an output voltage having ideal pulse-like voltage waveform H as shown in FIG. 10. By inputting this output voltage into a base of transistors 3 and 4, a voltage of DC power source 2 is made into a pulse form, and the feed-back voltage is input into transformer 5.

Such a conventional power source device has had a problem of a switching loss in a switching element. That is to say, in a power source device having a conventional configuration, a voltage is actually applied to each input end of comparator 10 in a way in which a noise voltage such as a ripple voltage is superimposed in addition to an ideal voltage waveform from voltage detecting circuit 9 and alternating signal generator 11. As a result, ideal pulse-like voltage waveform H shown in FIG. 10 may be changed.

This situation is described in detail with reference to FIG. 11. FIG. 11 is an enlarged view showing a voltage waveform to illustrate an operation of a conventional power source device. FIG. 11 is an enlarged view showing time interval “d” shown in FIG. 10. Although comparator 10 should obtain an output voltage of ideal pulse-like voltage waveform J as shown in FIG. 11, it actually obtains voltage waveform K having a large number of pulse-like waveforms in time interval “d”. Then, voltage waveform K is input into the base of switching elements 3 and 4. As a result, switching elements 3 and 4 carry out unnecessary switching operations. For example, transistor 3 carries out switching operations at times corresponding to the number of logical values high of voltage waveform K shown in FIG. 11, and transistor 4 carries out switching operations at times corresponding to the number of logical values low thereof. Accordingly, a switching loss is increased.

A power source device of the present invention includes an input terminal, a first switching element connected to the input terminal, a second switching element connected to the first switching element, a transformer including a primary side connected to a connecting node between the first and second switching elements, a low-pass filter including a series body of a coil and a capacitor connected to a secondary side of the transformer, an output terminal connected to a connecting node between the coil and the capacitor, a comparator having a first input end connected to the output terminal, and an alternating signal generator connected to a second input end of the comparator. An output terminal of the comparator is connected to control terminals of the first and second switching elements via a temporary amplitude generation permissible section.

According to such a configuration, by providing the temporary amplitude generation permissible section between the output end of the comparator and the control terminals of the first and second switching elements, an unnecessary switching operation is reduced and thus a switching loss can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a configuration of a power source device in accordance with a first exemplary embodiment of the present invention.

FIG. 2 is an enlarged view showing voltage waveforms to illustrate an operation of a power source device in accordance with the first exemplary embodiment of the present invention.

FIG. 3 is a circuit diagram illustrating a configuration of a power source device in accordance with a second exemplary embodiment of the present invention.

FIG. 4 is a circuit diagram showing a modification example of a power source device in accordance with the second exemplary embodiment of the present invention.

FIG. 5 is a circuit diagram illustrating a configuration of a power source device in accordance with a third exemplary embodiment of the present invention.

FIG. 6 is a circuit diagram illustrating a configuration of a power source device in accordance with a fourth exemplary embodiment of the present invention.

FIG. 7 is a circuit diagram illustrating a configuration of a power source device in accordance with a fifth exemplary embodiment of the present invention.

FIG. 8 is a circuit diagram illustrating a configuration of a power source device in accordance with a sixth exemplary embodiment of the present invention.

FIG. 9 is a circuit diagram illustrating a configuration of a conventional power source device.

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Previous Patent Application:
Switching control circuit and ac/dc converter using the same
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Harmonics related synchronization for switching regulators
Industry Class:
Electric power conversion systems

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